thomson chemistry experiment

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Cathode Ray Experiment

What is cathode ray tube.

A cathode-ray tube (CRT) is a vacuum tube in which an electron beam, deflected by applied electric or magnetic fields, produces a trace on a fluorescent screen.

The function of the cathode ray tube is to convert an electrical signal into a visual display. Cathode rays or streams of electron particles are quite easy to produce, electrons orbit every atom and move from atom to atom as an electric current.

Table of Contents

Cathode ray tube, recommended videos.

• J.J.Thomson Experiment

Apparatus Setup

Procedure of the experiment.

• Frequently Asked Questions – FAQs

In a cathode ray tube, electrons are accelerated from one end of the tube to the other using an electric field. When the electrons hit the far end of the tube they give up all the energy they carry due to their speed and this is changed to other forms such as heat. A small amount of energy is transformed into X-rays.

The cathode ray tube (CRT), invented in 1897 by the German physicist Karl Ferdinand Braun, is an evacuated glass envelope containing an electron gun a source of electrons and a fluorescent light, usually with internal or external means to accelerate and redirect the electrons. Light is produced when electrons hit a fluorescent tube.

The electron beam is deflected and modulated in a manner that allows an image to appear on the projector. The picture may reflect electrical wave forms (oscilloscope), photographs (television, computer monitor), echoes of radar-detected aircraft, and so on. The single electron beam can be processed to show movable images in natural colours.

J. J. Thomson Experiment – The Discovery of Electron

The Cathode ray experiment was a result of English physicists named J. J. Thomson experimenting with cathode ray tubes. During his experiment he discovered electrons and it is one of the most important discoveries in the history of physics. He was even awarded a Nobel Prize in physics for this discovery and his work on the conduction of electricity in gases.

However, talking about the experiment, J. J. Thomson took a tube made of glass containing two pieces of metal as an electrode. The air inside the chamber was subjected to high voltage and electricity flowing through the air from the negative electrode to the positive electrode.

J. J. Thomson designed a glass tube that was partly evacuated, i.e. all the air had been drained out of the building. He then applied a high electric voltage at either end of the tube between two electrodes. He observed a particle stream (ray) coming out of the negatively charged electrode (cathode) to the positively charged electrode (anode). This ray is called a cathode ray and is called a cathode ray tube for the entire construction.

The experiment Cathode Ray Tube (CRT) conducted by J. J. Thomson, is one of the most well-known physical experiments that led to electron discovery . In addition, the experiment could describe characteristic properties, in essence, its affinity to positive charge, and its charge to mass ratio. This paper describes how J is simulated. J. Thomson experimented with Cathode Ray Tube.

The major contribution of this work is the new approach to modelling this experiment, using the equations of physical laws to describe the electrons’ motion with a great deal of accuracy and precision. The user can manipulate and record the movement of the electrons by assigning various values to the experimental parameters.

A Diagram of JJ.Thomson Cathode Ray Tube Experiment showing Electron Beam – A cathode-ray tube (CRT) is a large, sealed glass tube.

The apparatus of the experiment incorporated a tube made of glass containing two pieces of metals at the opposite ends which acted as an electrode. The two metal pieces were connected with an external voltage. The pressure of the gas inside the tube was lowered by evacuating the air.

• Apparatus is set up by providing a high voltage source and evacuating the air to maintain the low pressure inside the tube.
• High voltage is passed to the two metal pieces to ionize the air and make it a conductor of electricity.
• The electricity starts flowing as the circuit was complete.
• To identify the constituents of the ray produced by applying a high voltage to the tube, the dipole was set up as an add-on in the experiment.
• The positive pole and negative pole were kept on either side of the discharge ray.
• When the dipoles were applied, the ray was repelled by the negative pole and it was deflected towards the positive pole.
• This was further confirmed by placing the phosphorescent substance at the end of the discharge ray. It glows when hit by a discharge ray. By carefully observing the places where fluorescence was observed, it was noted that the deflections were on the positive side. So the constituents of the discharge tube were negatively charged.

After completing the experiment J.J. Thomson concluded that rays were and are basically negatively charged particles present or moving around in a set of a positive charge. This theory further helped physicists in understanding the structure of an atom . And the significant observation that he made was that the characteristics of cathode rays or electrons did not depend on the material of electrodes or the nature of the gas present in the cathode ray tube. All in all, from all this we learn that the electrons are in fact the basic constituent of all the atoms.

Most of the mass of the atom and all of its positive charge are contained in a small nucleus, called a nucleus. The particle which is positively charged is called a proton. The greater part of an atom’s volume is empty space.

The number of electrons that are dispersed outside the nucleus is the same as the number of positively charged protons in the nucleus. This explains the electrical neutrality of an atom as a whole.

Uses of Cathode Ray Tube

• Used as a most popular television (TV) display.
• X-rays are produced when fast-moving cathode rays are stopped suddenly.
• The screen of a cathode ray oscilloscope, and the monitor of a computer, are coated with fluorescent substances. When the cathode rays fall off the screen pictures are visible on the screen.

Frequently Asked Questions – FAQs

What are cathode ray tubes made of.

The cathode, or the emitter of electrons, is made of a caesium alloy. For many electronic vacuum tube systems, Cesium is used as a cathode, as it releases electrons readily when heated or hit by light.

Where can you find a cathode ray tube?

Cathode rays are streams of electrons observed in vacuum tubes (also called an electron beam or an e-beam). If an evacuated glass tube is fitted with two electrodes and a voltage is applied, it is observed that the glass opposite the negative electrode glows from the electrons emitted from the cathode.

How did JJ Thomson find the electron?

In the year 1897 J.J. Thomson invented the electron by playing with a tube that was Crookes, or cathode ray. He had shown that the cathode rays were charged negatively. Thomson realized that the accepted model of an atom did not account for the particles charged negatively or positively.

What are the properties of cathode rays?

They are formed in an evacuated tube via the negative electrode, or cathode, and move toward the anode. They journey straight and cast sharp shadows. They’ve got strength, and they can do the job. Electric and magnetic fields block them, and they have a negative charge.

What do you mean by cathode?

A device’s anode is the terminal on which current flows in from outside. A device’s cathode is the terminal from which current flows out. By present, we mean the traditional positive moment. Because electrons are charged negatively, positive current flowing in is the same as outflowing electrons.

Who discovered the cathode rays?

Studies of cathode-ray began in 1854 when the vacuum tube was improved by Heinrich Geissler, a glassblower and technical assistant to the German physicist Julius Plücker. In 1858, Plücker discovered cathode rays by sealing two electrodes inside the tube, evacuating the air and forcing it between the electrode’s electric current.

Which gas is used in the cathode ray experiment?

For better results in a cathode tube experiment, an evacuated (low pressure) tube is filled with hydrogen gas that is the lightest gas (maybe the lightest element) on ionization, giving the maximum charge value to the mass ratio (e / m ratio = 1.76 x 10 ^ 11 coulombs per kg).

What is the Colour of the cathode ray?

Cathode-ray tube (CRT), a vacuum tube which produces images when electron beams strike its phosphorescent surface. CRTs can be monochrome (using one electron gun) or coloured (using usually three electron guns to produce red, green, and blue images that render a multicoloured image when combined).

How cathode rays are formed?

Cathode rays come from the cathode because the cathode is charged negatively. So those rays strike and ionize the gas sample inside the container. The electrons that were ejected from gas ionization travel to the anode. These rays are electrons that are actually produced from the gas ionization inside the tube.

What are cathode rays made of?

Thomson showed that cathode rays were composed of a negatively charged particle, previously unknown, which was later named electron. To render an image on a screen, Cathode ray tubes (CRTs) use a focused beam of electrons deflected by electrical or magnetic fields.

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Discovering the electron: JJ Thomson and the Cathode Ray Tube

Concept Introduction: JJ Thomson and the Discovery of the Electron

The discovery of the electron was an important step for physics, chemistry, and all fields of science. JJ Thomson made the discovery using the cathode ray tube. Learn all about the discovery, the importance of the discovery, and JJ Thomson in this tutorial article.

Further Reading on the Electron

Electron Orbital and Electron Shapes Writing Electron Configurations Electron Shells What are valence electrons? Electron Affinity Aufbau Principle

Who was JJ Thomson?

JJ Thomson was an English physicist who is credited with discovery of the electron in 1897. Thompson was born in December 1856 in Manchester, England and was educated at the University of Manchester and then the University of Cambridge, graduating with a degree in mathematics. Thompson made the switch to physics a few years later and began studying the properties of cathode rays. In addition to this work, Thomson also performed the first-ever mass spectrometr y experiments, discovered the first isotope and made important contributions both to the understanding of positively charged particles and electrical conductivity in gases.

Thomson did most of this work while leading the famed Cavendish Laboratory at the University of Cambridge. Although he received the Nobel Prize in physics and not chemistry, Thomson’s contributions to the field of chemistry are numerous. For instance, the discovery of the electron was vital to the development of chemistry today, and it was the first subatomic particle to be discovered. The proton and the neutron would soon follow as the full structure of the atom was discovered.

What is a cathode ray tube and why was it important?

Prior to the discovery of the electron, several scientists suggested that atoms consisted of smaller pieces. Yet until Thomson, no one had determined what these might be. Cathode rays played a critical role in unlocking this mystery. Thomson determined that charged particles much lighter than atoms , particles that we now call electrons made up cathode rays. Cathode rays form when electrons emit from one electrode and travel to another. The transfer occurs due to the application of a voltage in vacuum. Thomson also determined the mass to charge ratio of the electron using a cathode ray tube, another significant discovery.

How did Thomson make these discoveries?

Thomson was able to deflect the cathode ray towards a positively charged plate deduce that the particles in the beam were negatively charged. Then Thomson measured how much various strengths of magnetic fields bent the particles. Using this information Thomson determined the mass to charge ratio of an electron. These were the two critical pieces of information that lead to the discovery of the electron. Thomson was now able to determine that the particles in question were much smaller than atoms, but still highly charged. He finally proved atoms consisted of smaller components, something scientists puzzled over for a long time. Thomson called the particle “corpuscles” , not an electron. George Francis Fitzgerald suggested the name electron.

Why was the discovery of the electron important?

The discovery of the electron was the first step in a long journey towards a better understanding of the atom and chemical bonding. Although Thomson didn’t know it, the electron would turn out to be one of the most important particles in chemistry. We now know the electron forms the basis of all chemical bonds. In turn chemical bonds are essential to the reactions taking place around us every day. Thomson’s work provided the foundation for the work done by many other important scientists such as Einstein, Schrodinger, and Feynman.

Interesting Facts about JJ Thomson

Not only did Thomson receive the Nobel Prize in physics in 1906 , but his son Sir George Paget Thomson won the prize in 1937. A year earlier, in 1936, Thomson wrote an autobiography called “Recollections and Reflections”. He died in 1940, buried near Isaac Newton and Charles Darwin. JJ stands for “Joseph John”. Strangely, another author with the name JJ Thomson wrote a book with the same name in 1975. Thomson had many famous students, including Ernest Rutherford.

Discovery of the Electron: Further Reading

Protons, Neutrons & Electrons Discovering the nucleus with gold foil Millikan oil drop experiment Phase Diagrams

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Cathode Ray Experiment

The electric experiment by j.j. thomson.

J. J. Thomson was one of the great scientists of the 19th century; his inspired and innovative cathode ray experiment greatly contributed to our understanding of the modern world.

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• 3 Brownian Movement
• 4 Cathode Ray Experiment

Like most scientists of that era, he inspired generations of later physicists, from Einstein to Hawking .

His better-known research proved the existence of negatively charged particles, later called electrons, and earned him a deserved Nobel Prize for physics. This research led to further experiments by Bohr and Rutherford, leading to an understanding of the structure of the atom.

What is a Cathode Ray Tube?

Even without consciously realizing it, most of us are already aware of what a cathode ray tube is.

Look at any glowing neon sign or any ‘old-fashioned’ television set, and you are looking at the modern descendants of the cathode ray tube.

Physicists in the 19th century found out that if they constructed a glass tube with wires inserted in both ends, and pumped out as much of the air as they could, an electric charge passed across the tube from the wires would create a fluorescent glow. This cathode ray also became known as an ‘electron gun’.

Later and improved cathode ray experiments found that certain types of glass produced a fluorescent glow at the positive end of the tube. William Crookes discovered that a tube coated in a fluorescing material at the positive end, would produce a focused ‘dot’ when rays from the electron gun hit it.

With more experimentation, researchers found that the ‘cathode rays’ emitted from the cathode could not move around solid objects and so traveled in straight lines, a property of waves. However, other researchers, notably Crookes, argued that the focused nature of the beam meant that they had to be particles.

Physicists knew that the ray carried a negative charge but were not sure whether the charge could be separated from the ray. They debated whether the rays were waves or particles, as they seemed to exhibit some of the properties of both. In response, J. J. Thomson constructed some elegant experiments to find a definitive and comprehensive answer about the nature of cathode rays.

Thomson’s First Cathode Ray Experiment

Thomson had an inkling that the ‘rays’ emitted from the electron gun were inseparable from the latent charge, and decided to try and prove this by using a magnetic field.

His first experiment was to build a cathode ray tube with a metal cylinder on the end. This cylinder had two slits in it, leading to electrometers, which could measure small electric charges.

He found that by applying a magnetic field across the tube, there was no activity recorded by the electrometers and so the charge had been bent away by the magnet. This proved that the negative charge and the ray were inseparable and intertwined.

Thomson's Cathode Ray Second Experiment

Like all great scientists, he did not stop there, and developed the second stage of the experiment, to prove that the rays carried a negative charge. To prove this hypothesis, he attempted to deflect them with an electric field.

Earlier experiments had failed to back this up, but Thomson thought that the vacuum in the tube was not good enough, and found ways to improve greatly the quality.

For this, he constructed a slightly different cathode ray tube, with a fluorescent coating at one end and a near perfect vacuum. Halfway down the tube were two electric plates, producing a positive anode and a negative cathode, which he hoped would deflect the rays.

As he expected, the rays were deflected by the electric charge, proving beyond doubt that the rays were made up of charged particles carrying a negative charge. This result was a major discovery in itself, but Thomson resolved to understand more about the nature of these particles.

Thomson's Third Experiment

The third experiment was a brilliant piece of scientific deduction and shows how a series of experiments can gradually uncover truths.

Many great scientific discoveries involve performing a series of interconnected experiments, gradually accumulating data and proving a hypothesis .

He decided to try to work out the nature of the particles. They were too small to have their mass or charge calculated directly, but he attempted to deduce this from how much the particles were bent by electrical currents, of varying strengths.

Thomson found out that the charge to mass ratio was so large that the particles either carried a huge charge, or were a thousand times smaller than a hydrogen ion. He decided upon the latter and came up with the idea that the cathode rays were made of particles that emanated from within the atoms themselves, a very bold and innovative idea.

Later Developments

Thomson came up with the initial idea for the structure of the atom, postulating that it consisted of these negatively charged particles swimming in a sea of positive charge. His pupil, Rutherford, developed the idea and came up with the theory that the atom consisted of a positively charged nucleus surrounded by orbiting tiny negative particles, which he called electrons.

Quantum physics has shown things to be a little more complex than this but all quantum physicists owe their legacy to Thomson. Although atoms were known about, as apparently indivisible elementary particles, he was the first to postulate that they had a complicated internal structure.

Thomson's greatest gift to physics was not his experiments, but the next generation of great scientists who studied under him, including Rutherford, Oppenheimer and Aston. These great minds were inspired by him, marking him out as one of the grandfathers of modern physics.

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• J.J. Thomson - Facts

J.J. Thomson

Photo from the Nobel Foundation archive.

Joseph John Thomson The Nobel Prize in Physics 1906

Born: 18 December 1856, Cheetham Hill, United Kingdom

Died: 30 August 1940, Cambridge, United Kingdom

Affiliation at the time of the award: University of Cambridge, Cambridge, United Kingdom

Prize motivation: “in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases”

Prize share: 1/1

The idea that electricity is transmitted by a tiny particle related to the atom was first forwarded in the 1830s. In the 1890s, J.J. Thomson managed to estimate its magnitude by performing experiments with charged particles in gases. In 1897 he showed that cathode rays (radiation emitted when a voltage is applied between two metal plates inside a glass tube filled with low-pressure gas) consist of particles— electrons—that conduct electricity. Thomson also concluded that electrons are part of atoms.

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Key Questions

Thomson's experiments with cathode ray tubes helped him to discover the electron.

This ushered in a model of atomic structure referred to as the plum pudding model. I like to think of it like a sphere shaped chocolate chip cookie since plum pudding is not super popular in the US.

The cookie dough (they didn't know what it was yet) is positively charged and the chocolate chips (electrons) are negatively charged and scattered randomly throughout the cookie (atom). The positive and negative charges cancel producing a neutral atom.

. sought to determine the basic properties of the particles. Although he couldn't measure directly the mass or the electric charge of such a particle, he could measure how much the rays were bent by a magnetic field, and how much energy they carried. From this data he could calculate the of the mass of a particle to its electric charge ( / ). He collected data using a variety of tubes and using different gases. . Just as Emil Wiechert had reported earlier that year, the mass-to-charge ratio for cathode rays turned out to be far smaller than that of a charged hydrogen atom--more than one thousand times smaller. Either the cathode rays carried an enormous charge (as compared with a charged atom), or else they were amazingly light relative to their charge. was settled by . Experimenting on how cathode rays penetrate gases, he showed that if cathode rays were particles they had to have a mass very much smaller than the mass of any atom. The proof was far from conclusive. But experiments by others in the next two years yielded an independent measurement of the value of the charge ( ) and confirmed this remarkable conclusion. the hypothesis that "we have in the cathode rays matter in a new state, a state in which the subdivision of matter is carried very much further than in the ordinary gaseous state: a state in which all matter... is of one and the same kind; this matter being the substance from which all the chemical elements are built up."


1897 Experiments

J.J. Thomson

(1856-1940)

Who Was J.J. Thomson?

J.J. Thomson attended Trinity College at Cambridge, where he would come to head the Cavendish Laboratory. His research in cathode rays led to the discovery of the electron, and he pursued further innovations in atomic structure exploration. Thomson won the 1906 Nobel Prize in Physics, among many accolades.

Early Life and Education

Joseph John Thomson, who was always called J.J., was born in Cheetham Hill, England, near Manchester, in 1856. His father was a bookseller who planned for Thomson to be an engineer. When an apprenticeship at an engineering firm couldn't be found, Thomson was sent to bide his time at Owens College at the age of 14. In 1876, he received a small scholarship to attend Trinity College at Cambridge to study mathematics.

Thomson worked in the Cavendish Laboratory after graduation, under the tutelage of Lord Rayleigh. He quickly earned a membership in the prestigious Royal Society and was appointed Rayleigh’s successor as the Cavendish Professor of Physics at the age of 28. He was both respected and well-liked, and students came from around the world to study with him.

In 1894, Thomson began studying cathode rays, which are glowing beams of light that follow an electrical discharge in a high-vacuum tube. It was a popular research topic among physicists at the time because the nature of cathode rays was unclear.

Thomson devised better equipment and methods than had been used before. When he passed the rays through the vacuum, he was able to measure the angle at which they were deflected and calculate the ratio of the electrical charge to the mass of the particles. He discovered that the ratio was the same regardless of what type of gas was used, which led him to conclude that the particles that made up the gases were universal.

Thomson determined that all matter is made up of tiny particles that are much smaller than atoms. He originally called these particles 'corpuscles,' although they are now called electrons. This discovery upended the prevailing theory that the atom was the smallest fundamental unit.

In 1906, Thomson began studying positively charged ions, or positive rays. This led to one of his other famous discoveries in 1912 when he channeled a stream of ionized neon through a magnetic and an electric field and used deflection techniques to measure the charge to mass ratio. In doing so, he discovered that neon was composed of two different kinds of atoms, and proved the existence of isotopes in a stable element. This was the first use of mass spectrometry.

Personal Life and Later Years

Thomson married Rose Paget, one of his students, in 1890. They had one daughter, Joan, and one son, George Paget Thomson, who went on to become a physicist and win a Nobel Prize of his own. J.J. Thomson published 13 books and more than 200 papers in his lifetime. In addition to being awarded the Nobel Prize in 1906, he was knighted in 1908 by King Edward VII. He left research in 1918 to become Master of Trinity College. He died in Cambridge on August 30, 1940, and is buried in Westminster Abbey near two other influential scientists: Isaac Newton and Charles Darwin.

QUICK FACTS

• Name: Joseph John Thomson
• Birth Year: 1856
• Birth date: December 18, 1856
• Birth City: Cheetham Hill, Manchester
• Birth Country: England
• Gender: Male
• Best Known For: J.J. Thomson was a Nobel Prize-winning physicist whose research led to the discovery of electrons.
• Education and Academia
• Writing and Publishing
• Science and Medicine
• Astrological Sign: Sagittarius
• Owens College
• Trinity College
• Death Year: 1940
• Death date: August 30, 1940
• Death City: Cambridge
• Death Country: England

CITATION INFORMATION

• Article Title: J.J. Thomson Biography
• Author: Biography.com Editors
• Website Name: The Biography.com website
• Url: https://www.biography.com/scientists/jj-thomson
• Access Date:
• Publisher: A&E; Television Networks
• Last Updated: May 26, 2021
• Original Published Date: April 2, 2014
• To the electron: may it never be of any use!

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Thomson's Discovery of The Electron

This topic is part of the HSC Physics course under the section  Structure of The Atom .

HSC Physics Syllabus

investigate, assess and model the experimental evidence supporting the existence and properties of the electron, including:

How Did Thomson Discover The Electron?

This video describes Thomson's experiment that led to the discovery of the first subatomic particle – the electron.

J.J. Thomson’s Experiment

Thomson's experiment involved manipulating the path of a cathode ray using a uniform electric field and a uniform magnetic field. Thomson's experiment obtained a value for the charge to mass ratio of cathode rays, which proved their particle nature. 

In the first part of Thomson's experiment, a pair of charged metal plates was used to create a uniform electric field. When a cathode ray travelled through this field, it was deflected towards the positive plate. 

Next, Thomson applied a uniform magnetic field using current-carrying coils. The direction of this magnetic field was perpendicular to the electric field, and positioned such that it would cause the cathode ray to deflect downwards.

Thomson adjusted the strength of the magnetic field until the cathode travelled a straight path. When this occurred, the force acting on the cathode ray due to the electric field balanced the force due to the magnetic field.

$$F_E=F_B$$

$$qE=qvB\sin\theta$$

$$v=\frac{E}{B}$$

After a straight trajectory was achieved, the electric field was switched off. Under the influence of the magnetic field only, the cathode ray was deflected downwards. Here, the radius of the cathode's curved path can be analysed by considering centripetal force.

The centripetal force was provided by the force due to the magnetic field:

$$\frac{mv^2}{r}=qvB$$

$$\frac{mv}{r}=qB$$

Expressing  v in terms of  E and  B

$$\frac{m(\frac{E}{B})}{r}=qB$$

$$\frac{q}{m}=\frac{E}{rB^2}$$

(We recommend understanding the derivation of the above equation to be able to provide mathematical support in exam responses)

Since the value of  E ,  B and  r were known to Thomson, the value of the charge to mass ratio of the cathode ray was calculated. This value was 1.76 x 10 11 C kg –1

Thomson replicated the experiment using cathodes made from different metals and under various conditions. He showed that the value of charge to mass ratio remained constant. 

Thomson's Interpretation

Since an actual charge to mass ratio value was determined for cathode rays, Thomson proved that cathode rays do indeed have mass, and hence are negatively charged particles .

In addition, the constancy of the cathode ray's charge to mass ratio shows that these negatively charged particles are present in all matter. As a result, Thomson's experiment led to the discovery of the first subatomic particle – the electron. 

The charge to mass ratio of electrons was shown to be 1800 times greater than that of hydrogen ions. Thomson assumed the magnitude of charge is equal for these particles, leading to the conclusion that the mass of an electron is 1800 times smaller than a hydrogen ion.

Thomson's Model of the Atom ('Plum Pudding' Model)

The discovery of the electron as a subatomic particle led to the development of Thomson's atomic model.

A simple representation of Thomson's atomic model

In Thomson's model of the atom, negatively charged electrons are dispersed in a positive mass due to electrostatic repulsion. The electrons are held together in the atom due to their attraction to the positive mass.

One major limitation of Thomson's model is the lack of explanation for the positive mass. This feature of the model was based on theory and lacked experimental evidence.

Thomson's model of the atom was shown to be incorrect in Geiger-Marsden's gold foil experiment .

Previous Section:  Cathode Ray Experiments

Next Section:  Rutherford's Atomic Model

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J.J. Thomson Atomic Theory and Biography

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Sir Joseph John Thomson or J.J. Thomson is best known as the man who discovered the electron.

J.J. Thomson Biographical Data

Tomson was born December 18, 1856, Cheetham Hill, near Manchester, England. He died August 30, 1940, Cambridge, Cambridgeshire, England. Thomson is buried in Westminster Abbey, near Sir Isaac Newton. J.J. Thomson is credited with the discovery of the electron , the negatively charged particle in the atom . He is known for the Thomson atomic theory.

Many scientists studied the electric discharge of a  cathode ray tube . It was Thomson's interpretation that was important. He took the deflection of the rays by the magnets and charged plates as evidence of "bodies much smaller than atoms." Thomson calculated these bodies had a large charge-to-mass ratio and he estimated the value of the charge itself. In 1904, Thomson proposed a model of the atom as a sphere of positive matter with electrons positioned based on electrostatic forces. So, he not only discovered the electron but determined it was a fundamental part of an atom.

Notable awards Thomson received include:

• Nobel Prize in Physics (1906) "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases" 
• Knighted (1908)
• Cavendish Professor of Experimental Physics at Cambridge (1884–1918)

Thomson Atomic Theory

Thomson's discovery of the electron completely changed the way people viewed atoms. Up until the end of the 19th century, atoms were thought to be tiny solid spheres. In 1903, Thomson proposed a model of the atom consisting of positive and negative charges, present in equal amounts so that an atom would be electrically neutral. He proposed the atom was a sphere, but the positive and negative charges were embedded within it. Thomson's model came to be called the "plum pudding model" or "chocolate chip cookie model". Modern scientists understand atoms consist of a nucleus of positively-charged protons and neutral neutrons, with negatively-charged electrons orbiting the nucleus. Yet, Thomson's model is important because it introduced the notion that an atom consisted of charged particles.

Interesting Facts About J.J. Thomson

• Prior to Thomson's discovery of electrons, scientists believed the atom was the smallest fundamental unit of matter.
• Thomson called the particle he discovered 'corpuscles' rather than electrons.
• Thomson's master's work,  Treatise on the motion of vortex rings , provides a mathematical description of William Thomson's vortex theory of atoms. He was awarded the Adams Prize in 1884.
• Thomson discovered the natural radioactivity of potassium in 1905.
• In 1906, Thomson demonstrated a hydrogen atom had only a single electron.
• Thomson's father intended for J.J. to be an engineer, but the family did not have the funds to support the apprenticeship. So, Joseph John attended Owens College in Manchester, and then Trinity College in Cambridge, where he became a mathematical physicist. 
• In 1890, Thomson married one of his students, Rose Elisabeth Paget. They had a son and a daughter. The son, Sir George Paget Thomson, received the Nobel Prize in Physics in 1937.
• Thomson also investigated the nature of positively-charged particles. These experiments led to the development of the mass spectrograph.
• Thomson was closely aligned with chemists of the time. His atomic theory helped explain atomic bonding and the structure of molecules. Thomson published an important monograph in 1913 urging the use of the mass spectrograph in chemical analysis.
• Many consider J.J. Thomson's greatest contribution to science to be his role as a teacher. Seven of his research assistants, as well as his own son, went on to win the Nobel Prize in Physics. One of his best-known students was Ernest Rutherford , who succeeded Thomson as Cavendish Professor of Physics.
• Biography of Ernest Rutherford
• Famous Scientists Who Contributed to Chemistry
• Biography of Amedeo Avogadro, Influential Italian Scientist
• Biography of John Dalton, the 'Father of Chemistry'
• John Dalton's Atomic Theory
• Biography of Pierre Curie, Influential French Physicist, Chemist, Nobel Laureate
• Robert Hooke Biography (1635 - 1703)
• Biography of Dmitri Mendeleev, Inventor of the Periodic Table
• How to Measure Volume and Density
• Women in Chemistry - Famous Female Chemists
• Profiles of Famous Black Scientists
• 11 Black Chemists and Chemical Engineers
• Who Is the Father of Chemistry?
• Nobel Prize in Chemistry
• Famous Scientist Pictures - C Names
• A Brief History of Atomic Theory

Mathematics & Natural Sciences

The Great Principles of Chemistry

6 h total length

Learn how chemistry deepens our understanding of the natural world.

It’s amazing to consider that the vast beauty and complexity of nature is built upon the structure and interaction of atoms. 

Our new course, “ The Great Principles of Chemistry ,” will help you understand the reality of the material world through an exploration of the elements, a history of the great discoveries of chemistry, and an examination of the structure and behavior of atoms.

Join Dr. Matthew Young, the dean of natural sciences and a professor of chemistry at Hillsdale College, to discover the stories of great scientists who have furthered our understanding of the elements and the patterns and surprises that emerge from their discoveries. 

In “ The Great Principles of Chemistry ,” you’ll learn: 

• how chemistry fits into the liberal arts, 
• why the periodic table is structured the way it is and how it was filled out, 
• what discoveries led to the modern atomic theory, 
• how electrons behave and their role in forming ionic and covalent bonds, 
• and, the relationship between atomic structures and the natural order. 

And you will gain a greater appreciation for nature and the impact of chemistry on our world today!

Even if you’ve been intimidated by these subjects before, Dr. Young’s unique approach makes chemistry accessible to anyone as he teaches what everyone should know about chemistry.

The course includes nine lectures, each approximately 30 minutes long. You can receive a completion certificate for the course by watching the lecture videos, submitting a short quiz after each lecture, and passing a comprehensive course quiz at the end. You will also have access to optional study guides and a discussion board to supplement your learning.

Join Dr. Young in this free, self-paced course to discover why chemistry is the central science. 

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Lessons in this course.

Chemistry and the Liberal Arts

Chemistry is the study of matter and the changes it can undergo. The technical knowledge gained through chemistry has provided mankind with immense power, and thus it is best studied as part of a liberal arts education.   

The Discovery of Elements and the Periodic Table

Since the ancient Greeks, men have sought to understand the fundamental substances of matter. The discovery of the elements was advanced by the alchemists of the Middle Ages and exploded after Antoine Lavoisier set the foundation for chemistry in the late eighteenth century. The rapid gains in knowledge about matter led scientists to pursue a way to order the elements, which culminated in the development of the periodic table.  

Atomic Theory

Beginning in the late eighteenth century, scientists undertook a series of experiments that revealed three important laws about matter: the law of the conservation of matter, the law of definite proportions, and the law of multiple proportions. John Dalton used these three laws to publish the first modern atomic theory. 

Atomic Models

In 1897, J.J. Thomson discovered the first subatomic particle, the electron, as a result of his cathode ray experiment. Thomson’s initial model of the atom was later replaced by Ernest Rutherford’s discovery of the nucleus of an atom.  

The Strange Behavior of Electrons

Electrons behave in some ways as particles and in other ways as waves. They do not move in fixed orbits in the way that most particles do.  

Atomic Orbitals

The movement of electrons around the nucleus of an atom are described by wave functions associated with specific energy levels and orbitals around the nucleus. The patterns found in quantum mechanics undergird the structure of the periodic table. 

Ionic Bonds

The outermost electrons of an atom are called valence electrons. How full an atom's outer shell of valence electrons is determines its reactivity and ability to bond with another atom. An ionic bond forms when a valence electron is transferred from one atom to another.  

Covalent Bonds

G.N. Lewis developed the idea of covalent bonding where atoms bond together to form a molecule by sharing pairs of valence electrons. Covalent bonds occur between non-metal atoms to allow each to achieve a stable outer shell of electrons. 

The Molecular Basis of Life

As we study the molecules responsible for life, it is also important to recognize the limits of chemistry. Science cannot answer all of life’s questions, but it can give great insight into the natural world. 

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Enroll in this free online course on chemistry today!

What Current Students Are Saying

The course presents complex topics in a concise and intuitive manner. More importantly it promotes wonder, beautifully conveying the depth of the subject and encouraging further investigation beyond the videos.

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